Multi-channel tunable laser has been focus in the industry in recent years. Tunable laser products have been widely used in 10 Gb/s and 40 Gb/s optical communication system. These applications mainly use multi-channel tunable laser product with semiconductor integration technology (SGDBR). However, applications of the coherent optical communication system with a rate of over 100 Gb/s raised higher demands for multi-channel tunable laser, that is, it required tunable laser with narrow linewidth feature, because system characteristics are restricted by signal phase noise. Therefore, external-cavity laser with great linewidth control ability is becoming popular, in terms of applications of the coherent optical communication system with a rate above 100 Gb/s, typical example of which is thermo-optical tuning micro-optics external-cavity laser by the EMCORE company with linewidth smaller than 100 kHz, which has been preferred product in 100 Gb/s coherent optical communication system. It is a kind of external-cavity laser based on double thermo-optical tunable etalon, and realizes multi-channel tuning function through thermo-optical vernier adjustment. However, heat is a physical quantity that is hard to be controlled precisely. Thus thermo-optical tuning needs high-precision temperature calibration, and the thermal relaxation occurred during the tuning process often affects the tuning speed and control precision of the device.
In fact, traditional tunable external-cavity laser technology has developed for many years, such as typical semiconductor tunable external-cavity laser with Littman and Littrow structure, which are tunable structures based on grating dispersion and mechanical movement system of the resonant cavity. Many kinds of solid tunable lasers with high frequency stabilization use this sort of structure, which is relatively mature now. However, due to the intrinsic structure and tuning demands of these lasers, it is difficult to adapt to the requirements of optical communication system for small volume, long-term stability and reliability. Key problem therein is volume of the device. With development of micro-machine (MEMS) technology, solution of using MEMS device to realize the mirror movement tuning function in Littman structure has been proposed (refer to US patents including U.S. Pat. No. 6,847,661, U.S. Pat. No. 6,856,632, U.S. Pat. No. 6,912,235 by the Iolon company and U.S. Pat. No. 7,443,891 by the Coherent Company of US). Characteristics of them are using electrostatic MEMS driving mechanism to realize rotation of reflex endoscope. However, reflecting mirror and electrostatic driving machine thereof are not in a same plane, so this kind of MEMS mechanism appears too enormous and complicated, with low yield, high production cost and relatively poor environmental adaptability.
FIG. 2 is a schematic diagram of the principle of optical path of the existing technology of Littman tunable laser. In order to improve the wavelength or product rate control precision of the laser, traditional Littman tunable laser has slightly large beam spot, and the endoscope at the adjustment side plane thereof has relatively large area. The tuning of the wavelength or frequency of the laser is realized through the rotation of the endoscope on end face. Since area of endoscope is large enough, it has good adaptability to tuning of the broadband.